Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$104.61	11.827%	$116.9822	$116.98	$117.00	$117.00
Purchase #2	$175.26	6.418%	$186.5082	$186.51	$186.50	$186.50
Purchase #3	$223.63	11.550%	$249.4593	$249.46	$249.45	$249.50
Purchase #4	$223.61	10.558%	$247.2187	$247.22	$247.20	$247.20
Purchase #5	$196.91	6.471%	$209.652	$209.65	$209.65	$209.70
Purchase #6	$18.40	12.113%	$20.6288	$20.63	$20.65	$20.60
Purchase #7	$54.45	8.436%	$59.0434	$59.04	$59.05	$59.00
7 purchase totals =	$996.87		$1,089.4926	$1,089.49	$1,089.50	$1,089.50